The invention concerns a gear wheel or gear segment having a heavy load capability where the tooth root between two adjacent teeth takes the form, in the longitudinal direction, of a concave fillet running approximately in the direction of the rolling element generator line or of a tangent to the rolling element, and the tooth top in the longitudinal tooth direction, has a shape equidistant to the tooth root of the mating wheel in its operating position.
The general trend toward lightweight construction has also led, in gear wheel and transmission production, to constantly decreasing power weight ratios of the transmissions, i.e. to maximum possible power transmission with minimum overall height. A significant example of this is to be found in the differential gear units in vehicle rear axles. The tooth surface load capability is of secondary importance for these differential gear units. The determining feature for overall height is to be found solely in the dedendum load capability. The saving in weight is of considerable importance for these transmission units as they belong to the unsprung masses of a vehicle.
To reduce the power weight ratio two methods have been used until now, on the one hand, optimization of the fillet and on the other hand, taking advantage of the possibilities of materials such as, for example, case hardening, etc. These possibilities have, to a large extent, been exhausted and a limit has been reached which can no longer be exceeded with the technical means presently available.
An attempt has already been made to increase dedendum load capability by making the tooth roots concave and the apex of the teeth convex in the direction of the tooth face width (German Pat. No. 317 280). The increase in load capability with this gear wheel, however, is unsatisfactory as is described in detail below. The same applies to the bevel gear known from German Offenlegungsschrift No. 2 053 789 where the tooth spaces are provided with lateral reinforcement sections which extend at right angles to the tooth spaces and connect adjacent teeth to one another.